Dual purpose carrier wave receiver



Aug. 25, 1953 G. MOUNTJOY DUAL PURPOSE CARRIER WAVE RECEIVER Filed Nav. 50. 1949 HTTORNE'Y Patented Aug. 25, 1953 DUAL PURPOSE CARRIER WAVE RECEIVER Garrard Mountjoy, Canandaigua, N. Y., assignor to Stromberg-Carlson Company,

of New York a corporation Application November so, 1949, serialNo. 130,288

8 Claims.

The present invention relates to dual-purpose carrier-Wave receivers, and more particularly to a receiver capable of selectively receiving television broadcasts and frequency-modulation broadcasts.

In the conventional television receiver, a separate intermediate-frequency amplifier is provided for the sound carrier Wave which, according to the present American standards, is frequency-modulated and occupies a bandwidth approximately 50 kilocycles Wide. This sound-carrier intermediate-frequency amplifier supplies a conventional discriminator, which converts the modulated carrier signal to an audible frequency signal. If the tuner of such a conventional television receiver is adapted to cover the spectrum of frequencies Within which frequency-modulation broadcasts are'transrnitted, it is a relatively simple matter to adapt the television receiver for the reception of such broadcasts. For this purpose, the tuner is tuned to the carrier frequency of the desired frequency-modulation broadcast station, and the received signal is amplified in the sound-carrier intermediate-frequency ampliiier of the receiver and passed through the discriminator. The latter unit is preferably modifled in a manner which permits it to handle the somewhat Wider bandwidth of the frequencymodulation signal. Beyond these minor modifications, the conventional television receiver need not be changed in order to permit the reception of frequency-modulation broadcasts.

Recently, television receivers of the so-called intercarrier type have been introduced. A receiver of this type is disclosed, for example, in Parker Patent 2,448,908, issued September 7, 1948. In the intercarrier system of television reception, the picture and sound carrier waves are amplified together in a single intermediate-frequeneyl amplier. This amplifier has a relatively Wide band-pass characteristic in order to accommodate the picture signal carrier. At the output of the picture second detector there appears a beat note which corresponds with the difference in frequency between the picture and sound carriers. This beat note is frequency-modulated in accordance with the sound signal and is, at least to some extent, amplitude-modulated in accordance With the picture signal. By passing this beat note through a frequency-modulation detector Which is relatively insensitive to amplitude modulation, thesound modulation may be separated from the picture modulation and utilized in the customary manner, after suitable amplication, to operate a loud speaker. It will be (Cl. TIS-5.8)

apparent that, since an intercarrier television rece1ver does not have a separate intermediatefrequency amplifier of relatively narrow bandpass characteristic, such a receiver is not readily utilized for the reception of frequency-modulation broadcasts even if its tuner is designed to cover the frequency spectrum of such broadcasts.

It is an object of the present invention to provide a dual-purpose carrier-wave receiver which is selectively adapted for the reception of a first class of relatively wide-band signals and of a second class of relatively narrow-band signals.

It is another object of the present invention to provide a television receiver which is selectively adapted for the reception of frequencymodulation broadcasts.

Still another object of the invention is to provide, in a television receiver of the intercarrier type, means for selectively `receiving frequencymodulation broadcasts.

A further object of the present invention is to provide a carrier-wave receiverof simplied construction which is adapted selectively to receive television broadcasts or frequency-modulation broadcasts.

In accordance with the present invention, there is provided a superheterodyne receiver of the type adapted to receive a rst class of relatively Wide-band signals, thisreceiver comprising a tuner adapted to cover a range of frequencies including at least one spectrum of this first class of signals and a `second spectrum comprised of a second class of relatively narrow-band signals. The receiver also includes a relatively broad-band intermediate-frequency amplier and a first discriminator responsive to the first class of signals. In combination with this receiver, there are provided means for selectively rendering the receiver capable of reception of the second class of signals. These means comprise means for introducing a relatively narrow-band lter between the tuner and the intermediate-frequency ampli- Iier and means for simultaneously substituting a second discriminator for the rst discriminator, the second discriminator being responsive to the second class of signals.

In accordance with another feature of the present invention, the means for rendering the receiver capable of reception of the second class of signals are actuated by the tuning means of the receiver when the tuning means is adjusted to cover the second spectrum of signals.

Still another feature of the present invention is to provide, in combination with a superheterodyne receiver of the intercarrier type, simple and efficient means for selectively rendering the receiver capable of reception of frequency-modulation broadcasts. If desired, such means may be arranged to be actuated automatically when the tuning means of the receiver is adjusted to cover' a range of frequencies including the frequencymodulation broadcast spectrum.

The above and other objects and features of the present invention will be better understood by referring to the following description taken in connection with the accompanying drawing, in which like reference numerals designate like components and in which:

Fig. 1 is a block diagram of a' dual-purpose carrier-wave receiver in accordance withy the present invention; and

Fig. 2 is a schematic diagram of a portion of the receiver of Fig. 1.

Referring now to Fig. 1 of the drawing', there is shown a superheterodyne television receiver of the intercarrier type, modied in accordance with the present invention. The receiver of Fig. 1 includes a tuner I0, comprising a radio-frequency amplifier unit II, a mixer unit I2 and an oscillator unit I3. The signals received by an antenna I4 are supplied to radio-frequency amplifier unit II. Units II, I2 and I3 are preferably ganged, as indicated by broken line I5, for simultaneous adjustment, to permit tuner I to be tuned over a range of frequencies including at least one spectrum used for television broadcasts and at least one spectrum used for frequency-modulation broadcasts.

r)The output of tuner unit II) is supplied to a switch and filter unit I6 which in turn supplies an intermediate-frequency amplifier unit Il having a relatively broad band-pass characteristic. The output of unit I'I is supplied to a video detector unit I8 whichrin turn supplies a video Y amplier unit I9. The output of video amplier unit I9 is supplied to a conventional picture or cathode-ray tube 20.

The output of video amplifier I9 is also supplied to a .television sound discriminator unit 2l. The output of discriminator 2| is connected to a first terminal 22 of ya single-pole, double-throw switch 23, the movable arm 24 of which is connected to an audio-frequency amplifier 25, the output of which supplies a conventional loud speaker 26. The output of intermediate-frequency amplifier I1 is also supplied to a frequency-modulation discriminator 2'I, the output of which is connected to a second terminal 28 of switch 23.

Switch and filter unit I6 and switch 23 are preferably ganged together for simultaneous op-eration, as Vindicated by broken line 33. 1f desired, these units may also be ganged for actuation by tuning unit I0, as indicated by dot and dash line 34.

As shown in Fig. 1, the receiver is adjusted for the reception of television signals, `and its operation for this purpose is conventional. When adjusted for television reception, the filter of unit I6 is not in use, and so there is no interference with the passage of both the sound and picture carrier waves produced by mixer I2 and supplied to intermediate-frequency amplifier I'I. Switch 23 is in its upper position as shown, so that the beat note due to the interaction of the two carrier waves passes through television sound discriminator 2l, and the resultant audio-frequency wave is supplied to audio-frequency amplifier 25 and reproduced by loud speaker 26.

Now let it be assumed that switch 23 is thrown to its downward position, and that a corresponding adjustment of unit I6 has been made so that the filter of this unit is introduced between mixer I2 and intermediate-frequency amplifier II. Tuner I0 is now adjusted for the reception of a signal lying in the frequency-modulation broadcast spectrum. The lter of unit I6 has a relatively narrow band-pass characteristic which is centered around the nominal mid-frequency of the pass band of intermediate-frequency amplifier I'I. Thus, by the combined action of the filter of unit I6 and intermediate-frequency amplier II, the frequency-modulation carrier wave at the output of mixer` unit I2 is selectively amplied and other undesired signals which may be present are effectively eliminated. The resultant amplied frequency-modulation carrier Wave is supplied to frequency-modulation discriminator 21 the output of which, due to the position of switch 23, is supplied to audio-frequency amplifier 25 and thence to loud speaker 26.

In a particular embodiment in accordance with Fig. 1 and adapted for use under present-day lAmerican broadcast standards, tuner unit I0 might be designed to cover either or both of the television frequency spectrums of 54-88 megaeycles and 174-216 megacycles, either continuously or in channel-width steps, as well as the frequency-modulation spectrum of 88-108 megacycles. The filter of unit I6 might have a bandpass characteristic approximately 200 kilocycles wide centering around approximately 24 meg-acycles. Intermediate-frequency amplifier II might have a band-pass characteristic with a width of approximately 4 megacycles about a nominal mid-frequency of 24 megacycles. Television sound discriminator 2| would be responsive to a bandwidth of approximately 50 kilocycles with a mid-frequency of 4.5 megacycles, and frequency-modulation discriminator 21 would have a bandwidth of approximately 200 kilocycles centered about approximately 24 megacycles.

For the purposes of this application, it is assumed that discriminators 2l and 21 preferably include means for minimizing or substantially eliminating amplitude fluctuations. For example, if the discriminator itself is of the Foster- Seeley type, it may be preceded by one or more limiter stages. nator unit may comprise a ratio detector. The particular internal arrangements of discriminators 2i and 27 do not constitute part of the present invention.

Fig. 2 is a schematic diagram of one form which switch and ilter unit I6 of Fig. 1 may take. The input from mixer unit I2 (Fig. l) is supplied to an input terminal 4U, to which is connected an inductor 4I which, in combination with an inductor 42 and a capacitor 43, forms a bandpass filter 44 broadly tuned to a mid-frequency approximately corresponding to the mid-frequency of intermediate-frequency amplifier I'I (Fig. l). A resistor 45 is connected between the upper terminal of inductor 42 and ground, and

serves to adjust the band-pass characteristics of iilter 44.

The lower terminal of inductor 4I is connected through a radio-frequency choke coil 46 to a source 4l of positive potential, it being assumed that terminal 40 is conductively connected to the anode of an electron discharge device (not shown) comprising a portion of mixer unit I2. The junction of inductor 4I and choke coil 46 is connected to the movable arm .48 of a singlepole, double-throw switch 49, one terminal 50 0f,

As an alternative, the discrimiwhich is connected to the junction of inductor 42` and capacitor 43, andthe other terminal of which is connected through a blocking capacitor` 52 and an adjustable inductor 53 to aitap 54 on an inductor 55, the lower terminal of which is grounded as indicated.

A capacitor 56 is shunted across inductor`55, and an inductor 51, shunted by a capacitor 58, is coupled to inductor 55. One terminal of inductor 51 is grounded as indicated, and the otherterminal is connected to a rst terminal 59 of a single-pole, double-throw switch 60. The other terminal 6| of switch 60 is connected to the `junction of inductor 42 and resistor 45. The movable arm 62 of switch 60 is connected to an output terminal 63, which in turn is connected to the input of intermediate-frequency amplifier l1 (Fig. l). Switches 49and 6U may be ganged for simultaneous operation, as indicated by broken line 64.

Circuit elements 55, 56, 51 and 56 comprise a lightly damped network which has a relatively narrow band-pass characteristic, as for example 200 kilocycles, centered about the nominal midfrequency of the band-pass characteristic of intermediate-frequency amplier l1 (Fig. `1). This mid-frequency may be approximately 24 megacycles. In operation for television reception, switches 49 and 60 are in the positions shown in Fig. 2, and circuit elements 4I, 42 and 43 operate to provide a desired coupling characteristic of the television carrier waves from input terminal 40 to output terminal 63. For reception of frequency-modulation` broadcasts, switches 49 and 69 are thrown to their lower positions, so that circuit elements 55, 56, 51 and 58 serve to provide a relatively sharply tuned band-pass characteristic to permit the desired frequency-modulation signal to pass from input terminal 40 to output terminal 63 `and to provide a substantial degree of attenuation for other undesired signals.

It will be understood that both the television and the frequency-modulation filter arrangements shown by way of example in Fig. 2 are merely illustrative of the type of circuit congurations which are satisfactory for this purpose. Modifications may be made in either or both of these filters without departing from the scope of the present invention.

While there has been described what is at present considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and i scope of the invention.

What is claimed is:

1. The combination with a superheterodyne receiver of the type adapted to receive a rst class of relatively wide-band signals, said receiver comprising a tuner adapted to cover a range of frequencies including at least one spectrum of said first class of signals and a second spectrum comprised of a second class of relatively narrow-band signals, a relatively broad-band intermediatefrequency amplier and a first discriminator responsive to said rst class of signals, of means for selectively rendering said receiver capable of reception of said second class of signals, said means comprising means for inserting a relatively narrow-band filter between said tuner and said amplifier, and means for substituting, simultaneously with said insertion of said lter, a second discriminator `for said rst discriminator, said sec@ ond discriminator being responsive to said sec-` ceiver of the type adapted to receive a first classi of relatively Wide-band signals, said receiver comprising a tuner having tuning means adjustable to cover a range of frequencies including at least one spectrum of said first class of signals and a second spectrum comprised of a second class of relatively narrow-band signals, a relatively broadband intermediate-frequency amplifier and a first discriminator responsive to said first class of signals, of means actuated by said tuning means when adjusted to cover said second spectrum for rendering said receiver capable of reception of said second class of signals, said means comprising means for inserting a relatively narrow-band filter between said tuner and said amplifier, and means for substituting, simultaneously with said insertion of said iilter, a second discriminator for said rst discriminator, said second discriminator being responsive to said second class of signals.

3. The combination with a superheterodyne receiver of the type adapted to receive a iirst class of signals each comprising a pair of spaced carriers, said receiver comprising a tuner adapted to cover a range of frequencies including at least one spectrum of said first class of signals and a second spectrum comprised of a second class of signals each having a single carrier, an intermediate-frequency amplifier adapted to handle signals of said iirst class and a rst discriminator responsive to the frequency difference between said spaced carriers, of means for selectively rendering said receiver capable` of reception of said second class of signals, said means compr'ming means for inserting a iilter adapted to handle signals of said second class between said tuner and said amplier, and means for substituting, simultaneously with said insertion of said filter, a second discriminator for said lirst discriminator, said second discriminator being responsive to the frequency resulting from the hetrodyning of said single carrier frequency.

. 4. The combination with a superheterodyne receiver of the type adapted to receive a rst class of signals each comprising a pair of spaced carriers, said receiver comprising a tuner having tuning means adjustable to cover a range of frequencies including at least one spectrum of said first class of signals and a second spectrum comprised of a second class of signals each having a single carrier, an intermediate-frequency ampliiier adapted to handle signals quency difference between said spaced carriers, of means actuated by said tuning means when adjusted to cover said second spectrum for rendering said receiver capable of reception of said second class of signals, said means comprising means for inserting a filter adapted to handle signals of said second class between said tuner and said amplier, and means for substituting, simultaneously with said insertion of said filter, a second discriminator for said rst discriminator, said second discriminator being responsive to the frequency resulting from the heterodyning of said single carrier frequency.

5. The combination with a superheterodyne receiver of the type adapted to receive a first class of relatively wide-band signals each comprising a pair of spaced carriers, said receiver comprising a tuner adapted to cover a range of frequencies including at least one spectrum of said first class of said rst class and a rst discriminator responsive to the fre-Y of signals and aT second spectrum comprised of a second class of relatively narrow-band signals each having a single carrier, an intermediate-frequency amplifier adapted to handle signals of said iirst class and a; first discriminator responsive to the frequency difference between said spaced carriers, of means for selectively rendering said receiver capable of reception of said second class of signals, said means comprising means for inserting a relatively narrow-band lter between said tuner and said ampliiier, and means for substituting, simultaneously with said insertion of said filter, a second discriminator for said first discriminatorI said second discriminator being responsive to the frequency resulting from thev heterodyning of said single carrier frequency'.

6. The combination with a superheterodyne receiver of the type adapted to receive a first class of relatively wide-band signals each comprising a pair of spaced carriers, said receiver comprising a tuner having tuning, means adjustable to cover a range of frequencies including at least one spectrum of said first class of signals and a second spectrum comprised of a second class of relatively narrow-band signals each having a single carrier, an intermediate-frequency amplifier adapted to handle signals of said first class and a Afirst discriminator responsive to the irequency difference between said spaced carriers, of means actuated by said tuning means when adjusted to cover said second spectrum for rendering said receiver capable of reception of said second class of signals, said means comprising means for inserting a relatively narrow-band filter between said tuner and said amplifier, and means for substituting, simultaneously with said insertion of said lter, a second discriminator for said first discriminator, said second discriminator being responsive to the frequency resulting from the heterodyning of said single carrier frequency.

7. The combination with a superheterodyne television receiver of the intercarrier type, said receiver comprising a tuner adapted to cover a range of frequencies including a frequency-modulation broadcast spectrum, a relatively broadband intermediate-frequency amplifier, a video detector, an intercarrier sound discriminator fed with signals derivedl from said video detector, and an audio amplifier, of means for selectively rendering said receiver capable of reception of frequency-modulation broadcasts, said means comprising means for inserting a relatively narrow-band iilter between said tuner and said intermediate-frequency amplifier, a frequencymodulation discriminator connected tothe output f said intermediate-frequency ampli-fier,` and means for altering, simultaneously with said insertion of said filter, the connection of the input of said audio amplifier from said intercarrier sound discriminator output to theV output of said frequency-modulation discriminator.

8. The combination with a superheterodyne television receiver of the intercarrier type, said receiver comprising a tuner having tuning means adjustable to cover. a range of frequencies including at least one television broadcast spectrum and a frequency-modulation broadcast spectrum,y a relatively broad-band` intermediate-frequency amplifier a video detector,y and an intercarri-er sound discriminator fed with signals derived from said video detector, andan audio amplifier, of means actuated by said tuning means when adjusted to cover said frequency-modulationibroadcast spectrum for rendering said receiver capable of reception of frequency-modulation broadcasts, said means comprising. means for inserting a relatively narrow-band filter between said tuner and said intermediate-frequency amplifier, a frequency-modulation discriminator connected to the output of said intermediate-frequency amplifier, and means forV altering, simultaneously with said insertion of said filter, the connection of the input of said audio amplifier from said intercarrier sound output to the output of said frequency modulation detector.

GARRARD MOUNTJ OY References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Schematic Diagram for Admiral Combination Chassis 20 Al with 4J 1 FM-AM Radio Tuner.

Chassis, May 20, 1949. (Supplement to Service Letter No. 84, Copy Div. 16.) 

